CRITICAL DEBRIS FLOW ANALYSIS PARAMETERS - VELOCITY

Estimates of flow velocity are important for sizing debris flow mitigation channels, berms, walls and basins. Debris flow velocity influences run-out distance and impact force and is therefore reflective of a level of potential damage. Equations for predicting and measuring debris flow velocities are numerous, and often rely on parameters that cannot be measured with precision or have an unknown consistency of measurement. In addition, due to the large number of equations, it is difficult to know which best to apply to different conditions. Therefore, a preliminary study has been performed to assess the accuracy and precision of such equations.

The methods of calculating debris flow velocities were divided into three groups based on similarity of calculation and input parameters. Each group was evaluated using published measurements, video data, and recently collected field measurements. An analysis of accuracy and precision was completed from these evaluations and key sources of error were identified in each group. From this information, recommendations are made to improve field measurements and to select appropriate methods of debris flow velocity calculation.